Diamonds have inherent characteristics, such as non-conductivity, great hardness, high thermal conductivity, high heat resistance, and excellent chemical stability. Using these characteristics, diamonds have been applied to various fields, such as electronic devices and sensor materials, materials related to biotechnology, materials related to optics, and wear-resistant materials. A diamond compact is applied to, for example, a finishing cutting tool, an ultra-precision machining tool or the like by taking advantage of the hardness and wear resistance or the like; then such tools can be expected to have excellent cutting performance.
Then, as a production method of such a diamond compact, Patent Document 1, for example, shows a method of producing a diamond compact. In the method proposed by the document,    a mixture of carbonates and of organic compounds which form a supercritical fluid phase is used as a sintering aid;    the mixture is stacked up between the diamond layers; and then    the stacked layers are sintered under the conditions of high pressure and high temperature of 2000° C. or higher.Under such conditions, the diamond is thermodynamically stable.
In this production method, for example, oxalic acid dihydrate is used as an organic compound to form the above-mentioned supercritical fluid phase. However, oxalic acid dihydrate is a hazardous material, and needs to be mixed with carbonate in advance in order to prepare the sintering aid. Therefore, handling them is difficult, and this difficulty has been the obstacle to the attempt to use this method practically.
Patent Document 2, for example, also shows another production method. In order to remove silicate from the natural diamond powder during the final process of the method, the document proposes the steps in which:    an aqueous solution of pH 3 to 5 containing the diamond powder in a dispersed state, is poured into a vessel, and is shaken with quick movements; then,    the aqueous solution into which the diamond powder has been dispersed is frozen in the vessel using liquid nitrogen; further,    the diamond powder prepared by such a freeze-drying process is sintered together with the sintering aid of carbonate mixed with organic compounds (oxalic acid dihydrate), at a temperature of 1700° C. or higher, using an ultra high pressure/high temperature apparatus.
In this production method, the secondary particle formation in the diamond powder as a raw material for sintering can be considerably reduced. Thus, a relatively homogeneous diamond compact can be obtained. However, since this production method also requires the freeze-drying process, the preliminary arrangements become complicated. Additionally, the problem of the organic compound (oxalic acid dihydrate) being used as a sintering aid which has to be mixed in advance, persists.